Electrolytic desulphonation of anthraquinone sulphonic acids



1929- A. J. HAILWOOD 1,724,928

ELECTROLYTIC DESULPHONATION OF ANTHRAQUINONE SULPHONIC ACIDS Filed Dec.8, 1926 INVEN TOR Fl J, HAILWOOD by K? we Patented Aug. 20, 1929.

IJNITED STATES.

PATENT OFFICE.

ANTHONY JAMES H AILWOOD, OI BLACKLEY, MANCHESTER, ENGLAI ID, ASSIGNOB TOBRITISH DYESTUFFS CORPORATION LIMITED, OF MANCHESTER, LANCASHIRE,

ENGLAND.

ELECTROLYTIC DESULPHONATIQN OF AHTHRAQUINONE SULPHONIG ACIDS.

Application filed December a, 1926, Serial No.

The desulphonation of anthraquinone sul honic acids has previously beencarried out by heating solutions of the acids in 80 per cent sulphuricacid to high temperatures with the addition of mercury as a catalyst. Inow find that by electrolytic reduction of the sodium or potassium saltsof anthraquinone sulphonic acids in a divided cell, in alkalinesolution, those acid groups occupying a-positions are in great partremoved and replaced by hydrogen, while those ,B-positions arescarcely-affected. I find that under the reducing conditions of thecathode chamber reduction of the carbonyl groups of the anthra 'uinoneresidue readily takes place so that the, product from which thea-SlllPhODlC acid groups have been removed is found in the cathodesolution as an oxanthrol. In alkalinesolution a current of air suflicesto oxidize this to the anthraquinone in Whichform it is usually desiredand separated. ,I find also from my work that under the conditions Iuse,the desulphonation is largely subsequent 'to reduction to theoxanthrol, and because in the alkaline medium the oxanthrol is easilyoxidized back to the quinone by air, it is necessary to exclude air oroxygen as much as possible from the cathode chamber in order to ensureeflicient working. Many different metals or alloys may be used ascathode; for example, mercury or amalgamated copper. The current densitymay be varied withm wide limits, an advantageous currentdensity being2-3 amperes per square decimetre. The quantity of electricity requiredis usually about 1.4 times that required by theory, due allowance beingmade for the two atoms of hydrogen required to reduce each molecule ofanthraquinone to the corresponding oxanthrol. Although the processproceeds well at ordinary temperatures, it is advantageous in most casesto carry out the operations at a higher temperature, particularly if thesalts of the anthraquinone sulphonic acid or 153,473, and in GreatBritain April 15, 1926.

oxanthrol sulphonic acid are sparingly soluble in the catholyte. Theseparation of the cathode and anode solutions may be achieved lthel byusing a porous division of the pot type, or an impermeable divisionwhich clips into a mercury trap connecting the two solutions and whichserves as cathode.

In the accompanying drawing, there is shown in longltudinalcross-section an apparatus for conducting the electrolysis. A receptacleor beaker 10 is provided with a porous pot-11, in the bottom of which isplaced a layer 12- of mercury serving as the cathode. Above the mercuryis the catholyte 13, the composition of which-is explained more fullybelow. The pot 11 is provided with an airtight cover 14 through whichpasses a stirrer 15, an incased wire 16 leading to the mercury 12, and avent tube 17 permitting the escape of gases generated during theelectrolysis. It

will, of course, be understood that the essential elements containedwithin the porous pot 11, and forming a portion of the entire apparatus,constitute the dathode chamber. Surrounding the cathode chamber is theanolyte 18 of sodium hydroxid solution, into which extend anodes 19.

The following examples are intended to ill'istrate. the nature of myinvention but I do not limit myself to the particular details thereofExample 1.25 grams disodium anthraquinone-1:5-disulphonate are dissolvedin 1 litre of hot water containing 14 grams of sodium hydrate solution.The solution so obtained is introduced into a cathode chamber, whichconsists of a porous pot on the bottom of which is a layer of mercuryserving as the cathode. The porous pot is fitted with an air-tight lidthrough which passes a stirrer, a cathode lead and a tube to carry offexcess hydrogen. -The cathode chamber is surrounded by a 25 per centaqueous'solution of sodium hydrate which acts as the anolyte.

' passed until about 1317 ampere-hours have OiNa ONa ' +NaOH (LNa Theanthraquinone is filtered off, washed with water and dried. It isalready very pure and may be obtained quitepure by a single 'sublination or recrystallization for example from toluene. The yield ofanthraquinone is about 70 per cent calculated on the disulphonic acidused. In addition, there is an appreciable quantity of mono-sulphonicacid left in the solution.

Ewa'rr'tple 2.-11 grams of the dipotassium' salt ofanthraquinone-l:8-disulphonic acid, 6 grams potassium chloride and 300grams of water forms the catholyte and a 10 per cent aqueous solution ofpotassium carbonate 25 forms the anolyte. The cell-arrangement-is thesame as in Example 1, a mercury cathode being used. The temperatureconditions are the same as before and 6 ampere-hours of electricity at acurrent density of 2 amperes per square decimetre are passed. Theproduct is worked up as in Example 1.

' Example 3.300 cc. of a 2.2 per cent solution of the disodium salts of1:6- and 1:7- disulphonic acids of anthraquinone containing smallquantities of the sodium salts of the SOaN L excess H01 4- o y ebeta-naphthylamine The reaction is as follows: 10

ONa SOzNa NazSO:

+ NazSO;

1 5- and '1 8- disulphonic acids obtained .as a waste product, aretreated with 4.2 grams of sodium hydrate and subjected to electrolyticreduction in the cathode chamber of the cell described in Example 1under the same conditions. After 3.5 ampere-hours of electrlclty areused, the brownish-red solution is oxidized with a current of air andfiltered 3NaCl oo Example 4.- 5 grams of the sodium salt of in 300 cc.water containing 4.2 grams of soanthraqumone-a-sulphonic acid aredissolved dium hydrate in solution and the product is subjected toelectrolysis, as in Example 1, 2 5, ampere-hours of electricitybeing'used. The product is oxidized by air as before described. Theanthraquinone produced is filtered otl', washed with Water, and dried.The yield is 66 per cent of theory. What I claim and desire to secure byLetters Patent is 1. A process for the manufacture of oxanthrolderivatives from anthraquinone compounds containing a-sulphonic acidgroups, consisting in the reduction of, and the removal of sucha-SlllPllOIllC acid groups from, such anthraquinone compounds byelectrolytic reduction in alkaline solution.

2. A process for the manufacture of anthraquinone and anthraquinonecompounds derivatives from compounds containing asulphonic acidgroupsthereof, consisting in the reduction of, and the removal of sucha-sulphonic acid groups from. such anthraquinone by electrolyticreduction in alkaline solution to produce oxanthrol derivatives,followed by oxidation of the resulting oxanthrol followed by oxidationof the resulting oxanthrol derivatives, substantially as described. i

In testimonv whereof'I afiix my signature.

ANTHONY JAMES HAILWOOD.

